Polishing head and polishing apparatus

ABSTRACT

A polishing head comprising an annular rigid ring; a rubber film attached to the rigid ring by using uniform tensile force; a back plate that is connected to the rigid ring and forms a space portion with the rubber film and the rigid ring; and an annular template that is provided at a peripheral portion of a lower surface portion of the rubber film concentrically with the rigid ring and configured to hold an edge portion of a workpiece, the polishing head holding a back surface of the workpiece on the lower surface portion of the rubber film and sliding a front surface of the workpiece on a polishing pad attached to a turn table to perform polishing. The polishing head and the polishing apparatus can be used for final polishing and uniformly polish the entire front surface regardless of the thickness of the template.

TECHNICAL FIELD

The present invention relates to a polishing head configured to hold aworkpiece at the time of polishing a front surface of a workpiece and apolishing apparatus including the polishing head, and more particularlyto a polishing head configured to hold a workpiece on a rubber film, anda polishing apparatus including this polishing head.

BACKGROUND ART

In recent years, higher integration of semiconductor devices placedemand for higher flatness of semiconductor wafers used in such devices.The higher flatness up to near the edge of wafers is also needed toraise the yield of semiconductor chips.

The shape of finished semiconductor wafers depends on a final mirrorpolishing process. For a 300-mm-diameter silicon wafer, in particular,primary polishing by double-side polishing is performed to meet strictspecifications of the flatness, and then secondary polishing and finishpolishing by single-side polishing is performed to remove scratches onthe surface or to improve surface roughness.

The secondary and finish polishing by single-side polishing is needed tomaintain or improve flatness obtained by the primary polishing bydouble-side polishing and to finish the front surface of a wafer into aperfect mirror-surface with no defects, such as scratches.

As shown in FIG. 10, a common single-side polishing apparatus includes aturn table 103 on which a polishing pad 102 is attached, apolishing-agent-supply mechanism 104, a polishing head 101, for example.Such a polishing apparatus 110 holds a workpiece W with the polishinghead 101, supplies a polishing agent 105 from the polishing-agent-supplymechanism 104 onto the polishing pad 102, rotates both the turn table103 and the polishing head 101, and polishes the workpiece W by bringinga front surface of the workpiece into sliding contact with the polishingpad 102.

Examples of a method of holding a workpiece with a polishing headinclude attaching the workpiece to a flat workpiece-holding boardthrough an adhesive such as wax, and using a polishing head 121 of awaxless type, shown in FIG. 11, that holds a workpiece W with aworkpiece-holding board 112 through a commercially available templateassembly 113 having a template 113 b, for preventing the workpiece fromcoming off, attached to an elastic film 113 a called a backing film.

Examples of the polishing head of a waxless type also include apolishing head 131, shown in FIG. 12, that includes a backing film 113 aattached on a workpiece-holding board 112, instead of the commerciallyavailable template, and an annular guide ring 113 b, for preventing aworkpiece from coming off, provided around the side surface of theworkpiece-holding board.

Although, the workpiece holding board 112 is commonly composed of ahighly-flat ceramic plate, this polishing head unfortunately has aproblem in that variation in thickness of the backing film 113 aproduces a small pressure distribution, resulting in waviness of thepolished front surface of the workpiece and hence lower flatness of theworkpiece.

Accordingly, there is also disclosed a polishing head by a rubber chuckmethod having a rubber film for holding a workplace in place of theworkpiece-holding board, in which the workpiece is pressed against apolishing pad by supplying pressurized fluid, such as air, to the backsurface of a rubber film to inflate the rubber film with an uniformpressure (see Patent Document 1, for example).

FIG. 13 schematically illustrates an example of a configuration of thepolishing head by the rubber chuck method. The polishing head 141 ismainly constituted of an annular rigid ring 144, made of e.g., SUS, arubber film 143 attached to the rigid ring 144, and a back plate 145connected to the rigid ring 144. The rigid ring 144, the rubber film143, and the back plate 145 define a sealed space 146. On a lowersurface portion of the rubber film 143, a backing film 148 is attached,and an annular template 147 is provided concentrically with the rigidring 144. The pressure in the space 146 is adjusted by supplying apressurized fluid to the center of the back plate 145 with apressure-adjusting mechanism 150. The back plate 145 is connected to apolishing head upper portion 149 having a pressing means (notillustrated) for pressing the back plate 145 toward the polishing pad.

CITATION LIST Patent Literature

-   Patent Document 1: Japanese Unexamined Patent Application    Publication No. 2008-110407

SUMMARY OF INVENTION Technical Problem

Such a polishing head by the rubber chuck method prevents the smallpressure distribution due to the variation in thickness of the backingfilm, and hence the waviness of the polished front surface of theworkpiece. Since the template has an inner diameter larger than an outerdiameter of the workpiece, there is disadvantageously a small gapbetween the template and the workpiece. At this gap between the templateand the workpiece, the rubber film inflates largely, when a pressurizedfluid is supplied into the space with the pressure-adjusting mechanismto adjust the pressure. This inflation increases the pressure at anouter peripheral portion of the workpiece. As a result, this outerperipheral portion tends to be polished excessively and thereby toproduce an outer peripheral sag.

Adjusting the thickness of the template allows the pressure at the outerperipheral portion of the workpiece to be adjusted to some extent, butvariation in thickness of the template varies a polishing stock removalof the outer peripheral portion; consequently, the flatness cannot bekept stable.

In final polishing of the workpiece, the template is preferably keptfrom contacting the polishing pad, because an extraneous substance,separated from the template when the template contacts a polishing padfor final polishing, creates a defect on the front surface of aworkpiece.

A polishing head, configured to have a thickness thinner than that of aworkpiece to avoid contact with a polishing pad, on the other hand,increases the pressure at the outer peripheral portion of the workpiece,thereby polishing the outer peripheral portion excessively to producethe outer peripheral sag and hence to lower the flatness of theworkpiece. Thus, this polishing head cannot be used for final polishing.

In view of the above-described problems, it is an object of the presentinvention to provide a polishing head and a polishing apparatus that canbe used for final polishing of the workpiece and polish the entire frontsurface of the workpiece uniformly regardless of the thickness of thetemplate: more specifically a polishing head and a polishing apparatus,configured to hold a back surface of a workpiece on a rubber film and tohold an edge portion of the workpiece by a template, that can polish theworkpiece uniformly up to the outer peripheral portion of the workpiecewithout creating surface defects, such as scratches, on the frontsurface of the workpiece, with the template configured to have athickness thinner than that of the workpiece to avoid contact with apolishing pad.

Solution to Problem

To achieve the problem, the present invention provides a polishing headcomprising an annular rigid ring; a rubber film attached to the rigidring with an uniform tensile force; a back plate connected to the rigidring, the back plate defining a space together with the rubber film, andthe rigid ring; and an annular template configured to hold an edgeportion of a workpiece, the template being provided concentrically withthe rigid ring in a peripheral portion on a lower surface of the rubberfilm and, the polishing head configured to hold a back surface of theworkpiece on the lower surface of the rubber film and to polish theworkpiece by bringing a front surface of the workpiece into slidingcontact with a polishing pad attached to a turn table, wherein anincompressible fluid is enclosed in the space.

Such a polishing head can appropriately adjust a surface shape of therubber film for holding the workpiece by the enclosed incompressiblefluid, and suppress local deformation of the surface shape duringpolishing of the workpiece, thereby polishing the entire front surfaceof the workpiece uniformly regardless of the thickness of the template.The polishing head can also be used for final polishing of a workpiece,because the polishing head can polish the entire front surface of theworkpiece uniformly with the template configured to have a thicknessthinner than that of the workpiece to avoid contact with a polishingpad.

The incompressible fluid may be water or an incompressible fluid whosemain component is water.

Such a polishing head can be configured at a low cost, and avoid a riskof contamination of the workpiece and the interior of a polishingapparatus, even when the incompressible fluid leaks from the space.

Alternatively, the incompressible fluid may be a polishing agent usedfor the polishing of the workpiece or an aqueous solution containing atleast one of components contained in the polishing agent.

Such a polishing head does not affect the polishing of the workpiece,even when the incompressible fluid leaks from the space.

The lower surface portion of the rubber film is preferably adjustablyinflated in accordance with a difference in thickness between thetemplate and the workpiece.

Such a polishing head can adjust a polishing stock removal of the outerperipheral portion of the workpiece, thereby surely polishing the entirefront surface of the workpiece uniformly.

The incompressible fluid is preferably enclosed under a pressure higherthan a polishing pressure applied during the polishing of the workpiece.

Such a polishing head can prevent the pressure to the outer peripheralportion of the workpiece from increasing, and polish the workpiece witha more uniform polishing load for the workpiece.

The rubber film is preferably attached to the rigid ring with the rubberfilm stretched by a tensile force of 30 N or more.

Such a polishing head can surely maintain the surface shape of therubber film after the incompressible fluid is enclosed during polishing,thereby surely polishing the entire front surface of the workpieceuniformly.

The rubber film is preferably composed of any one of isoprene rubber,styrene-butadiene rubber, chloroprene rubber, nitride-butadiene rubber,urethane rubber, fluororubber, silicon rubber, ethylene-propylenerubber, polyester elastomer, polysulphone resin, and grilamid resin.

Such a polishing head, which uses a sturdy material hard to tear withhigh tensile force, can maintain the surface shape of the rubber filmafter the incompressible fluid for a long time, thereby surely polishingthe entire front surface of the workpiece uniformly at a low cost.

The preset invention also provides a polishing apparatus used forpolishing a front surface of a workpiece, the apparatus comprising apolishing pad attached to an upper side of a turn table; apolishing-agent-supply mechanism configured to supply a polishing agentto an upper side of the polishing pad; and a polishing head configuredto hold the workpiece according to the present invention.

Such a polishing apparatus can appropriately adjust a surface shape ofthe rubber film for holding the workpiece by the enclosed incompressiblefluid, and suppress local deformation of the surface shape duringpolishing of the workpiece, thereby polishing the entire front surfaceof the workpiece uniformly regardless of the thickness of the template.The polishing apparatus can also be used for final polishing of aworkpiece, because the polishing head can polish the entire frontsurface of the workpiece uniformly with the template configured to havea thickness thinner than that of the workpiece to avoid contact with apolishing pad.

Advantageous Effects of Invention

The polishing head of the present invention includes an incompressiblefluid enclosed in the space. Such a polishing head can appropriatelyadjust a surface shape of the rubber film for holding the workpiece bythe enclosed incompressible fluid, and suppress local deformation of thesurface shape during polishing of the workpiece, thereby polishing theentire front surface of the workpiece uniformly regardless of thethickness of the template. The polishing head can also be used for finalpolishing of a workpiece, because the polishing head can polish theentire front surface of the workpiece uniformly with the templateconfigured to have a thickness thinner than that of the workpiece toavoid contact with a polishing pad.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing an example of a polishing head of thepresent invention;

FIG. 2A is explanatory views of a method for enclosing an incompressiblefluid in the case of using a template having a thickness thinner thanthat of a workplace;

FIG. 2B is explanatory views of a method for enclosing an incompressiblefluid in the case of using a template having a thickness larger thanthat of a workpiece;

FIG. 3 is a schematic view showing another example of a polishing headof the present invention;

FIG. 4 is a schematic view showing an example of a polishing apparatusof the present invention;

FIG. 5 shows results of Examples 1 to 3;

FIG. 6 shows results of Comparative Examples 1 to 3;

FIG. 7A shows polishing stock removal distribution of a workpiece inExamples 4 to 7;

FIG. 7B shows polishing stock removal distribution in the range from 120mm to 148 mm away from the center of the workpiece in Examples 4 to 7;

FIG. 8 is a view showing the relationship between tensile force appliedat the time of attaching a rubber film and variation in polishing stockremoval at the outer peripheral portion in Examples 4 to 7;

FIG. 9 is shows results of Examples 8 to 9;

FIG. 10 is a schematic view showing an example of a conventionalpolishing apparatus;

FIG. 11 is a schematic view showing an example of a conventionalpolishing head using a backing film;

FIG. 12 is a schematic view showing another example of the conventionalpolishing head using a backing film; and

FIG. 13 is a schematic view showing an example of a conventionalpolishing head by the rubber chuck method.

DESCRIPTION OF EMBODIMENTS

Although an embodiment according to the present invention will bedescribed below, the present invention is not restricted thereto.

There has been a problem in that the polishing stock removal at theouter peripheral portion of a workpiece varies depending on thethickness of a template and the flatness cannot be kept stable. Thethickness of the template needs to be equal to or larger than that ofthe workpiece to suppress outer peripheral sag. The template having sucha thickness, however, contacts a polishing pad to produce an extraneoussubstance, which may cause defects, such as scratches, on the frontsurface of the workpiece.

The present inventor repeatedly conducted keen examination to solve sucha problem, and conceived that a rubber chuck portion, for holding aworkpiece, which is configured in a manner that a rubber film isattached to an annular rigid ring with a uniform tensile force, a backplate is provided at an upper part to define a sealed space, and anincompressible fluid is enclosed into the sealed space. Thisconfiguration enables the workpiece to be polished into a flat workpieceregardless of the thickness of a template. The present inventor therebybrought the present invention to completion.

FIG. 1 illustrates an example of a polishing head of the presentinvention.

As illustrated in FIG. 1, the polishing head 1 includes an annular rigidring 4 composed of a rigid material such as SUS (stainless), a rubberfilm 3 attached to the lower surface of the rigid ring 4 with a uniformtensile force, and a back plate 5 provided on the upper surface of therigid ring 4.

The rigid ring 4, the rubber film 3, and the back plate 5 define asealed space 6.

Here, the material and the shape of the back plate 5 are not restrictedin particular, as long as the back plate 5 can define the space 6together with the rigid ring 4 and the rubber film 3.

An annular template 7 having an inner diameter slightly larger than anouter diameter of a workpiece W is provided concentrically with therigid ring 4 at the peripheral portion on the lower surface of therubber film 3. This template 7 is configured to hold an edge portion ofthe workpiece W, and provided so as to protrude downward along the outerperipheral portion of the lower surface portion of the rubber film 3.

The template 7 may be configured to have an outer diameter larger thanat least an inner diameter of the rigid ring 4 and an inner diametersmaller than the inner diameter of the rigid ring 4. Such aconfiguration enables the entire front surface of the workpiece to bepressed uniformly.

The template 7 is preferably composed of a material softer than theworkpiece W and resistant to wear, which is hard to wear by beingbrought into sliding contact with a polishing pad of a polishingapparatus during polishing, to avoid contamination, scratches, andimpressions of the workpiece W.

The polishing head, illustrated in FIG. 1 by way of example, includesthe template 7 having a thickness thinner than that of the workpiece W,but is not limited thereto. As illustrated in FIG. 3, the polishing headmay include a template 7 having a thickness equal to or larger than thatof the workpiece W.

A backing film 8 may be attached to at least a portion of the lowersurface of the rubber film 3 at which the workpiece W is held. Thebacking film 8 contains water to stick the workpiece W so that theworkpiece W is held on a workpiece-holding surface of the rubber film 3.The backing film 8 may be composed of polyurethane, for example. Thebacking film 8 containing water enables the workpiece W to be surelyheld by surface tension of the water.

A commercially available template assembly having a template attachedonto the backing film can be used.

In such a rubber chuck portion, constituted of the rubber film 3, therigid ring 4, the back plate 5, and others, an incompressible fluid 2 ispreliminarily enclosed in the space 6 before polishing the workpiece W.When the incompressible fluid 2 is enclosed, the surface shape of theworkpiece-holding portion of the rubber film 3 for holding the workpieceW is adjusted into an appropriate shape. A polishing head upper portion9 including a non-illustrated pressurizing means is mounted on the uppersurface of the back plate 5. The term “incompressible fluid” used in theinvention means a fluid of which the volume does not greatly reduce bycompression under pressure, unlike a gas.

As illustrated in FIG. 3, through holes 11 e and 11 b and couplers 10 aand 10 b may be provided in the back plate 5 to enclose the fluid 2 inthe space 6. The couplers 10 a and 10 b are capable of being connectedwith a later-described fluid enclosure apparatus.

The volume of the incompressible fluid 2 enclosed in the space 6 of thepolishing head of the invention hardly varies during polishing. Thepolishing head can therefore suppress deformation of the appropriatelyshaped surface of the rubber film 3, in particular, the local inflationof the rubber film 3 at the gap portion between the workpiece W and thetemplate 7 so that an uniform polishing load can be applied over theworkpiece W to polish the workpiece. As a result, the entire frontsurface of the workpiece can be uniformly polished, regardless of thethickness of the template 7. In addition, the polishing head enables theworkpiece W to be uniformly polished up to the outer peripheral portionwithout surface defects, such as scratches, on the front surface of theworkpiece W, and can thus be used for final polishing, even when thetemplate 7 having a thickness thinner than that of the workpiece W isused to avoid contact of the template 7 with a polishing pad of apolishing apparatus.

The incompressible fluid may be water or an incompressible fluid whosemain component is water.

Such an incompressible fluid enables the polishing head to be configuredat a low cost, and the polishing head does not contaminate a workpieceor the inside of a polishing apparatus, even when the incompressiblefluid leaks from the space, for example, due to tear of the rubber film.

For a workpiece of semiconductor material, pure water, which does notcontain metal ions, is preferably used as the incompressible fluid toprevent metal contamination, for example.

Alternatively, the incompressible fluid may be a polishing agent usedfor the polishing of the workpiece or an aqueous solution containing atleast one of components contained in the polishing agent.

Such a polishing head does not affect the polishing of the workpiece,even when the incompressible fluid leaks from the space.

A method for enclosing an incompressible fluid in the space will now bedescribed.

FIG. 2A illustrates an example of a method for enclosing the fluid whena template having a thickness thinner than that of a workpiece is used.

As illustrated in FIG. 2A, the polishing head 21 is provided with twothrough holes 11 a and 11 b in the upper surface of the back plate 5 tointroduce the incompressible fluid 2 into the space 6 and to dischargethe fluid from the space 6. Couplers 10 a and 10 b are provided at therespective through holes 11 a and 11 b to enclose the incompressiblefluid 2 in the space 6 while maintaining a pressure of theincompressible fluid 2 (also referred to as a enclosure pressure,hereinafter). When the incompressible fluid 2 is enclosed in the space 6before polishing the workpiece, a fluid enclosure apparatus is connectedto the polishing head as follows.

As illustrated in FIG. 2A, the fluid enclosure apparatus 30 has acircuit connecting with a pressure gauge 33 and a valve 32 a tointroduce the incompressible fluid 2. The circuit is connected with anipple 31 a at its terminal. This nipple 31 a is connected with thecoupler 10 a provided on the back plate 5. The fluid enclosure apparatus30 has a circuit having one terminal connected with a drain and a valve32 b connected at the middle of the circuit to discharge theincompressible fluid 2. The other terminal of this circuit is connectedwith a nipple 31 b. This nipple 31 b is connected with the coupler 10 bprovided on the back plate 5.

Then, a workpiece W or an adjustment plate 36 having the same thicknessas that of the workpiece W is placed on a flat base 35, and anadjustment spacer 34 having a thickness equal to a difference inthickness between the workpiece W and the template 7 is placed on thelower surface of the template 7. The polishing head components includingthe backing film 8, the template 7, the rubber film 3, the rigid ring 4,and the back plate 5 are placed on the base 35 such that the workpiece Wor the adjustment plate 36 is accommodated in a hole of the template V.The base 35 and the back plate 5 are then fixed by a clamp jig 37 toprevent the height of the back plate 5 from changing when theincompressible fluid 2 is enclosed.

The valves 32 a and 32 b are then opened to introduce the incompressiblefluid 2 into the space 6, and a degassing process is performed on thespace 6. The degassing process can be performed in such a manner thatthe terminal on the drain side is connected with a pressure reducingcircuit, then the valve 32 a is closed, and the valve 32 b is opened,for example.

The valves 32 a and 32 b are then closed, a non-illustratedpressure-adjusting mechanism for the incompressible fluid 2 adjusts suchthat the pressure gauge 33 exhibits a predetermined pressure. The valve32 a is then opened to introduce the incompressible fluid 2 into thespace 6. After confirming the pressure gauge 33 exhibits a predeterminedpressure, the valve 32 a is closed to enclose the incompressible fluid 2in the space 6. After enclosure, the nipples 31 a and 31 b are removedfrom the couplers 10 a and 10 b provided on the upper portion of theback plate 5.

In the enclosure of the fluid 2, the surface of the rubber film 3 isshaped by using the adjustment spacer 34 having a thickness thinner thana difference in thickness between the workpiece and the template, suchthat the inflation of the surface becomes small at the central part ofthe rubber film 3. Such an adjusted polishing head increases thepolishing pressure applied to the outer peripheral portion of theworkpiece, and thereby increases the polishing stock removal of theouter peripheral portion. On the contrary, the surface of the rubberfilm 3 is shaped by using the adjustment spacer 34 having a thicknessthicker than a difference in thickness between the workpiece and thetemplate, such that the inflation of the surface becomes large at thecentral part of the rubber film 3. Such an adjusted polishing headdecreases the polishing pressure applied to the outer peripheral portionof the workpiece, and thereby decreases the polishing stock removal ofthe outer peripheral portion. The polishing stock removal of the outerperipheral portion of the workpiece can be adjusted by adjusting thethickness of the adjustment spacer 34 used for enclosing the fluid asdescribed above.

FIG. 2B illustrates an example of a method for enclosing the fluid whena template having a thickness thicker than that of a workpiece is used.In this case, as illustrated in FIG. 2B, the adjustment spacer 34 isinserted below the lower surface of a workpiece W, and theincompressible fluid 2 can be enclosed in the same manner as above. Inthis case, the polishing stock removal of the outer peripheral portionof the workpiece can be also adjusted by adjusting the thickness of theadjustment spacer 34.

When the thickness of the workpiece is equal to that of the template,the incompressible fluid 2 may be enclosed without using the adjustmentspacer.

As described above, the lower surface portion of the rubber film ispreferably adjustably inflated in accordance with a difference inthickness between the template and the workpiece. Such a polishing headcan adjust a polishing stock removal of the outer peripheral portion ofthe workpiece, thereby surely polishing the entire front surface of theworkpiece uniformly.

The incompressible fluid is preferably enclosed under a pressure higherthan a polishing pressure applied during the polishing of the workpiece.The enclosure pressure can be adjusted by the above pressure-adjustingmechanism of the fluid enclosure apparatus, for example.

Such a polishing head can prevent the pressure to the outer peripheralportion of the workpiece from increasing, and polish the workpiece witha more uniform polishing load for the workpiece.

The rubber film is preferably attached to the rigid ring with the rubberfilm stretched by a high tensile force, particularly a tensile force of30 N or more, to maintain the surface shape formed as above by enclosingthe incompressible fluid.

Such a polishing head can surely maintain the surface shape of therubber film after the incompressible fluid is enclosed during polishing,thereby surely polishing the entire front surface of the workpieceuniformly.

The rubber film is preferably composed of a sturdy material that is hardto tear with high tensile force and resistant to creep deformation tomaintain its surface shape formed as above by enclosing theincompressible fluid for a long time.

Accordingly, the rubber film is preferably composed of any one ofisoprene rubber, styrene-butadiene rubber, chloroprene rubber,nitride-butadiene rubber, urethane rubber, fluororubber, silicon rubber,ethylene-propylene rubber, polyester elastomer, polysulphone resin, andgrilamid resin.

Such a polishing head can surely polish the entire front surface of theworkpiece uniformly, and reduce cost due to longer lifetime of therubber film.

A polishing apparatus of the present invention will now be described.

FIG. 4 schematically illustrates an example of a polishing apparatus ofthe present invention.

As illustrated in FIG. 4, the polishing apparatus 20 of the inventionincludes a polishing pad 22 attached to an upper side of a turn table23, a polishing-agent-supply mechanism 24 configured to supply apolishing agent 25 to an upper side of the polishing pad 22, and thepolishing head 21 of the invention configured to hold a workpiece W.This polishing head 21 can press the workpiece W against the polishingpad 22 attached to the turn table 23 by using a non-illustratedpressurization mechanism.

The front surface of workpiece W is polished by sliding the workpiecethrough rotation movement of the polishing head 21 coupled to a rotaryshaft and revolution movement of the turn table 23 while supplying thepolishing agent 25 onto the polishing pad 22 by thepolishing-agent-supply mechanism 24.

Such a polishing apparatus can suppress deformation of the surface shapeof the rubber film, particularly local inflation of the rubber film atthe gap between the workpiece and the template during polishing of theworkpiece, so that an uniform polishing load can be applied over theworkpiece W to polish the workplace. As a result, the entire frontsurface of the workplace can be uniformly polished, regardless of thethickness of the template. In addition, the polishing apparatus canpolish the entire front surface of the workpiece uniformly, even whenthe template having a thickness thinner than that of the workpiece isused. The polishing apparatus can thus be used for final polishing.

EXAMPLES

Although the present invention will now be more specifically explainedbased on examples and comparative examples hereinafter, the presentinvention is not restricted thereto.

Examples 1 to 3

A workpiece was polished with a polishing apparatus of the presentinvention including the polishing head as illustrated in FIG. 3, andvariation in polishing stock removal in a plane of the polishedworkpiece was evaluated. A silicon single crystal wafer having adiameter of 300 mm and a thickness of 775 μm was used as the workpieceW. The polishing stock removal was calculated by measuring both thethicknesses of the wafer before and after polishing with a flatnessmeasuring instrument in a region excluding a width 2 mm of the outermostperipheral portion as a flatness-guaranteed region and by obtainingdifferences between the thicknesses before and after polishing in across section of the wafer along a diametric direction. A flatnessmeasuring instrument (WaferSight) manufactured by KLA-Tencor was usedfor measuring the flatness.

The following polishing heads were prepared: A rigid ring composed ofSUS with an outer diameter of 360 mm and an inner diameter of 320 mm wasused. A rubber film composed of silicon rubber with a thickness of 1 mmand a rubber hardness of 90 degrees was attached to the lower surface ofthe rigid ring under a tensile force of 7.5 N. A commercially availabletemplate assembly was attached to the front surface of the rubber film.The template assembly has a template with an outer diameter of 355 mm,an inner diameter of 302 mm, and a thickness of 700 μm (Example 1), or athickness of 780 μm (Example 2), or a thickness of 800 μm (Example 3)attached to a surface of the backing film.

As illustrated in FIG. 2A, an incompressible fluid was then enclosedwith a fluid enclosure apparatus. At this time, an adjustment spacer of75 μM was inserted below the lower surface of the template when thethickness of the template was 700 μm, no adjustment spacer was used whenthe thickness was 780 μM, and an adjustment spacer of 25 μm was insertedbelow the lower surface of the wafer when the thickness was 800 μm. Purewater was used as the incompressible fluid, and the fluid was enclosedin the space under a pressure of 20 kPa.

The prepared polishing head was mounted on a polishing apparatus of theinvention as illustrated in FIG. 4, and the wafer was polished. It is tobe noted that both surfaces of the wafer were subjected to primarypolishing in advance, and the edge portion of the wafer was alsopolished in advance. A 800-mm diameter turn table and a regularly usedpolishing pad were used.

In the polishing, an alkali solution containing colloidal silica wasused as a polishing agent, and the polishing head and the turn tablewere each rotated at 30 rpm. A polishing load (pressing force) for thewafer was set to 20 kPa in terms of a contact pressure of the wafersurface by non-illustrated pressurizing means to polish the wafer. It isto be noted that a polishing time was adjusted such that an averagepolishing amount of the wafer was 1 μm.

FIG. 5 shows the polishing stock removal distribution of the waferpolished in each of Examples 1 to 3. As shown in FIG. 5, it can beunderstood that the polishing stock removal distribution of the waferwas substantially uniform and hardly dependent on the thickness of thetemplate unlike the later-described Comparative Examples 1 to 3. A rangeof the polishing stock removal in a cross section was 0.042 μm inExample 1, 0.027 μm in Example 2, and 0.048 μm in Example 3, which werebetter than those of the later-described Comparative Examples 1 to 3.

It was confirmed that the polishing head and the polishing apparatus ofthe invention enable the entire front surface of a wafer to be uniformlypolished, regardless of the thickness of a template.

Comparative Examples 1 to 3

A silicon single crystal wafer was polished under the same conditions asthose for Examples 1 to 3, with a polishing apparatus, as illustrated inFIG. 10, having a conventional polishing head, as illustrated in FIG.13, with no incompressible fluid of the invention. The rigid ring andthe template of the polishing head used had the same configuration asExamples 1 to 3. The used rubber film was composed of silicon rubberwith rubber hardness of 70 degrees, and attached to the lower surface ofthe rigid ring under a tensile force of 5 N.

In each of cases where the template having a thickness of 700 μm(Comparative Example 1) was used, the template having a thickness of 780μm (Comparative Example 2) was used, and the template having a thicknessof 800 μm (Comparative Example 3) was used, variation in polishing stockremoval in a plane of the polished wafer was evaluated.

FIG. 6 shows the polishing stock removal distribution of the waferpolished in each of Comparative Examples 1 to 3. As shown in FIG. 6, itcan be understood that the polishing stock removal distribution of thewafer is strongly dependent on the thickness of the template, the outerperipheral portion of the wafer is excessively polished in the case ofusing the template having a thickness smaller than the thickness of thewafer (Comparative Example 1), and the polishing stock removal of theouter peripheral portion of the wafer was low in the case of usingtemplate having a thickness larger than the thickness of the wafer(Comparative Example 3). The range of the polishing stock removal in across section was 0.181 μm in Comparative Example 1, 0.061 μm inComparative Example 2, or 0.104 μm in Comparative Example 3, which wereworse than those of the Examples 1 to 3.

Examples 4 to 7

A silicon single crystal wafer was polished under the same conditions asthose of Example 1 except that silicon rubber was attached underconditions of a tensile force of 5 N (Example 4), 20 N (Example 5), 35 N(Example 6), and 48 N (Example 7), and the variation in polishing stockremoval in a plane of the polished wafer was evaluated as with Example1.

FIG. 7A shows the polishing stock removal distribution of the waferpolished in each of Examples 4 to V. FIG. 7B shows the polishing stockremoval distribution in the range from 120 mm to 148 mm away from thewafer center as a polishing stock removal distribution of an outerperipheral portion of the wafer. As shown in FIGS. 7A and 7B, it can beunderstood that the wafer was polished uniformly up to the outerperipheral portion in each of Examples 4 to 7.

Additionally, as an index representing the polishing stock removaldistribution at the outer peripheral portion of the wafer, a differencebetween a maximum value and a minimum value of the polishing stockremoval in the range from 135 mm to 148 mm away from the water centerwas calculated, which is regarded as the variation in polishing stockremoval at the outer peripheral portion of the wafer. The variation inpolishing stock removal at the outer peripheral portion of the wafer was0.043 μm in Example 4, 0.027 μm in Example 5, 0.016 μm in Example 6, or0.011 μm in Example 7.

FIG. 8 shows a relationship between the tensile force of the siliconrubber and the variation in polishing stock removal at the outerperipheral portion of the wafer. As shown in FIG. 8, it can beunderstood that the variation in polishing stock removal at the outerperipheral portion of the wafer decreases as the tensile force of therubber increases. It can be also understood that, when the tensile forceis 30 N or more, the variation in polishing stock removal at the outerperipheral portion of the wafer becomes 0.020 μm or less, which meansthe outer peripheral portion of the wafer can be more uniformlypolished.

Examples 8 and 9

To examine an influence of a charging pressure of an incompressiblefluid, a silicon single crystal wafer was polished under the sameconditions as those of Example 7 except that a pressure at the time ofenclosure was set to 10 kPa (Example 8) or 40 kPa (Example 9) and apolishing head having pure water enclosed therein was used, and avariation in polishing stock removal in a wafer radial direction afterpolishing was evaluated as with Example 7.

FIG. 9 shows the polishing stock removal distribution at an outerperipheral portion of the wafer polished in each of Examples 8 and 9. Asdescribed above, the variation in polishing stock removal at the outerperipheral portion of the wafer in Example 7 was 0.011 μm, whereas thevariation in polishing stock removal at the outer peripheral portion ofthe wafer in Example 8 where the enclosure pressure is 10 kPa lower thanan enclosure pressure of 20 kPa for pure water in Example 7 was as highas 0.033 μm, and the variation in polishing stock removal at the outerperipheral portion of the wafer in Example 9 where the enclosurepressure for pure water is 40 kPa higher than that in Example 7 was aslow as 0.005 μm.

It was understood from this result that the variation in polishing stockremoval at the outer peripheral portion of the wafer can be reduced whenthe enclosure pressure of the incompressible fluid is set to a highpressure. When the enclosure pressure of the incompressible fluid is setto be higher than at least a polishing load of the wafer, the outerperipheral portion of the wafer can be further uniformly polished.

It is to be noted that the present invention is not limited to theforegoing embodiment. The embodiment is just an exemplification, and anyexamples that have substantially the same feature and demonstrate thesame functions and effects as those in the technical concept describedin claims of the present invention are included in the technical scopeof the present invention.

For example, the polishing head of the present invention is notrestricted to the conformations shown in FIGS. 1 and 3. For example, theshape of a main body of the polishing head can be appropriately designedexcept requirements described in claims. Additionally, the configurationof the polishing apparatus is not restricted to that shown in FIG. 4.For example, a polishing apparatus may be provided with a plurality ofpolishing heads of the present invention.

1-8. (canceled)
 9. A polishing head comprising an annular rigid ring; arubber film attached to the rigid ring with an uniform tensile force; aback plate connected to the rigid ring, the back plate defining a spacetogether with the rubber film, and the rigid ring; and an annulartemplate configured to hold an edge portion of a workpiece, the templatebeing provided concentrically with the rigid ring in a peripheralportion on a lower surface of the rubber film and, the polishing headconfigured to hold a back surface of the workpiece on the lower surfaceof the rubber film and to polish the workpiece by bringing a frontsurface of the workpiece into sliding contact with a polishing padattached to a turn table, wherein an incompressible fluid is enclosed inthe space.
 10. The polishing head according to claim 9, wherein theincompressible fluid is water or an incompressible fluid whose maincomponent is water.
 11. The polishing head according to claim 9, whereinthe incompressible fluid is a polishing agent used for the polishing ofthe workpiece or an aqueous solution containing at least one ofcomponents contained in the polishing agent.
 12. The polishing headaccording to claim 9, wherein the lower surface portion of the rubberfilm is adjustably inflated in accordance with a difference in thicknessbetween the template and the workpiece.
 13. The polishing head accordingto claim 10, wherein the lower surface portion of the rubber film isadjustably inflated in accordance with a difference in thickness betweenthe template and the workpiece.
 14. The polishing head according toclaim 11, wherein the lower surface portion of the rubber film isadjustably inflated in accordance with a difference in thickness betweenthe template and the workpiece.
 15. The polishing head according toclaim 9, wherein the incompressible fluid is enclosed under a pressurehigher than a polishing pressure applied during the polishing of theworkpiece.
 16. The polishing head according to claim 14, wherein theincompressible fluid is enclosed under a pressure higher than apolishing pressure applied during the polishing of the workpiece. 17.The polishing head according to claim 9, wherein the rubber film isattached to the rigid ring with the rubber film stretched by a tensileforce of 30 N or more.
 18. The polishing head according to claim 16,wherein the rubber film is attached to the rigid ring with the rubberfilm stretched by a tensile force of 30 N or more.
 19. The polishinghead according to claim 9, wherein the rubber film is composed of anyone of isoprene rubber, styrene-butadiene rubber, chloroprene rubber,nitride-butadiene rubber, urethane rubber, fluororubber, silicon rubber,ethylene-propylene rubber, polyester elastomer, polysulphone resin, andgrilamid resin.
 20. The polishing head according to claim 18, whereinthe rubber film is composed of any one of isoprene rubber,styrene-butadiene rubber, chloroprene rubber, nitride-butadiene rubber,urethane rubber, fluororubber, silicon rubber, ethylene-propylenerubber, polyester elastomer, polysulphone resin, and grilamid resin. 21.A polishing apparatus used for polishing a front surface of a workpiece,the apparatus comprising a polishing pad attached to an upper side of aturn table; a polishing-agent-supply mechanism configured to supply apolishing agent to an upper side of the polishing pad; and a polishinghead configured to hold the workpiece according to claim
 9. 22. Apolishing apparatus used for polishing a front surface of a workpiece,the apparatus comprising a polishing pad attached to an upper side of aturn table; a polishing-agent-supply mechanism configured to supply apolishing agent to an upper side of the polishing pad; and a polishinghead configured to hold the workpiece according to claim 20.